12:08 a.m.
Good afternoon
How can I use retract in action or exception handler?
For example,
0. I have a flow diagram;
1. in some node the fact Person( age == 10) is added to the working memory
by 'insert';
2. after some steps, the split node pass the control to the action-node
3. and in this action I need to retract this fact. How?!
The action MVEL code like:
$t : Person( age==10)
retract($t)
- does not work b/c of knowledge base errors:
"Could not parse knowledge... "
"Unable to build expression for action... "
"java.lang.Class cannot be cast to org.mvel2.util.MethodStub :
org.drools.lang.descr.ProcessDescr@fa54fe"
Thanks,
Eugene P
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7:57 a.m.
On 02/06/2010 23:08, EugeneP wrote:
Good afternoon
How can I use retract in action or exception handler?
For example,
0. I have a flow diagram;
1. in some node the fact Person( age == 10) is added to the working memory
by 'insert';
2. after some steps, the split node pass the control to the action-node
3. and in this action I need to retract this fact. How?!
The action MVEL code like:
$t : Person( age==10)
retract($t)
That would not be any valid MVEL or Java; you have mixed a rule LHS nd a
rule RHS - neither of which are valid for an action. Firstly you'll need
access to the facthandle, so you'll need to store that as a variable
some how. Then you can do
kcontext.knowledgeRuntime.retract( factHandle );
- does not work b/c of knowledge base errors:
"Could not parse knowledge..."
"Unable to build expression for action..."
"java.lang.Class cannot be cast to org.mvel2.util.MethodStub :
org.drools.lang.descr.ProcessDescr@fa54fe"
Thanks,
Eugene P
1:19 a.m.
Thanks, it helps.
But there are some more questions.
1. What is an official name of rule language, if it is not MVEL? Why "MVEL
dialect" in split constraints allow using code like:
$p: Person ( age > 21 )
2. Why it is not possible to use rules in actions in MVEL mode? I suppose it
would be useful.
3. How can I create new object in the constraint? For example, I have a
constraint:
$p : Person( age < 21 )
- in this branch I need to create the new object "PersonFault" and insert it
to the working memory, but the code :
$p : Person( age < 21 )
$fault = new PersonFault($p, "WRONG AGE");
kcontext.getKnowledgeRuntime().insert($fault);
- is not working. Nor in the constraint, nor in the action...
Regards,
EugeneP
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12:19 p.m.
New subject: How can I use retract in action or exception handler?
Thanks, it helps.
But there are some more questions.
1. What is an official name of rule language, if it is not MVEL? Why "MVEL
dialect" in split constraints allow using code like:
$p: Person ( age > 21 )
DRL - presumably standing for Drools Rule
Language
2. Why it is not possible to use rules in actions in MVEL mode? I
suppose it
would be useful.
What do you actually mean by using a rule in an action..
The answer is likely to be it is due to the way that rules are declarative and not
procedural and how the Rete algorithm works.
3. How can I create new object in the constraint? For example, I have
a
constraint:
$p : Person( age < 21 )
- in this branch I need to create the new object "PersonFault" and insert it
to the working memory, but the code :
$p : Person( age < 21 )
$fault = new PersonFault($p, "WRONG AGE");
kcontext.getKnowledgeRuntime().insert($fault);
- is not working. Nor in the constraint, nor in the action...
It won't work in the constraint as it doesn't make sense to create objects in the
constraint.
The standard way to do it is as follows - also note the knowledge runtime methods are
exposed directly (see
http://downloads.jboss.com/drools/docs/5.0.1.26597.FINAL/drools-expert/ht...)
Rule "foo"
when
$p : Person(age < 21)
then
insert(new PersonFault($p, "WRONG AGE"));
end
Thomas
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11:05 p.m.
New subject: How can I use retract in action or exception handler?
I try to create the new object (in the constraint) for passing it to the
exception node's variable.
Can I create or set process variables in the constraint?
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5302
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4 comments
3 participants
participants (3)
-
EugeneP -
Mark Proctor -
Swindells, Thomas